diff --git a/lib/Sema/SemaLambda.cpp b/lib/Sema/SemaLambda.cpp
index 21202c1..468fa02 100644
--- a/lib/Sema/SemaLambda.cpp
+++ b/lib/Sema/SemaLambda.cpp
@@ -225,73 +225,153 @@
   }
 }
 
-static bool checkReturnValueType(const ASTContext &Ctx, const Expr *E,
-                                 QualType &DeducedType,
-                                 QualType &AlternateType) {
-  // Handle ReturnStmts with no expressions.
-  if (!E) {
-    if (AlternateType.isNull())
-      AlternateType = Ctx.VoidTy;
+/// If this expression is an enumerator-like expression of some type
+/// T, return the type T; otherwise, return null.
+///
+/// Pointer comparisons on the result here should always work because
+/// it's derived from either the parent of an EnumConstantDecl
+/// (i.e. the definition) or the declaration returned by
+/// EnumType::getDecl() (i.e. the definition).
+static EnumDecl *findEnumForBlockReturn(Expr *E) {
+  // An expression is an enumerator-like expression of type T if,
+  // ignoring parens and parens-like expressions:
+  E = E->IgnoreParens();
 
-    return Ctx.hasSameType(DeducedType, Ctx.VoidTy);
+  //  - it is an enumerator whose enum type is T or
+  if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
+    if (EnumConstantDecl *D
+          = dyn_cast<EnumConstantDecl>(DRE->getDecl())) {
+      return cast<EnumDecl>(D->getDeclContext());
+    }
+    return 0;
   }
 
-  QualType StrictType = E->getType();
-  QualType LooseType = StrictType;
+  //  - it is a comma expression whose RHS is an enumerator-like
+  //    expression of type T or
+  if (BinaryOperator *BO = dyn_cast<BinaryOperator>(E)) {
+    if (BO->getOpcode() == BO_Comma)
+      return findEnumForBlockReturn(BO->getRHS());
+    return 0;
+  }
 
-  // In C, enum constants have the type of their underlying integer type,
-  // not the enum. When inferring block return types, we should allow
-  // the enum type if an enum constant is used, unless the enum is
-  // anonymous (in which case there can be no variables of its type).
-  if (!Ctx.getLangOpts().CPlusPlus) {
-    const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E->IgnoreParenImpCasts());
-    if (DRE) {
-      const Decl *D = DRE->getDecl();
-      if (const EnumConstantDecl *ECD = dyn_cast<EnumConstantDecl>(D)) {
-        const EnumDecl *Enum = cast<EnumDecl>(ECD->getDeclContext());
-        if (Enum->getDeclName() || Enum->getTypedefNameForAnonDecl())
-          LooseType = Ctx.getTypeDeclType(Enum);
-      }
+  //  - it is a statement-expression whose value expression is an
+  //    enumerator-like expression of type T or
+  if (StmtExpr *SE = dyn_cast<StmtExpr>(E)) {
+    if (Expr *last = dyn_cast_or_null<Expr>(SE->getSubStmt()->body_back()))
+      return findEnumForBlockReturn(last);
+    return 0;
+  }
+
+  //   - it is a ternary conditional operator (not the GNU ?:
+  //     extension) whose second and third operands are
+  //     enumerator-like expressions of type T or
+  if (ConditionalOperator *CO = dyn_cast<ConditionalOperator>(E)) {
+    if (EnumDecl *ED = findEnumForBlockReturn(CO->getTrueExpr()))
+      if (ED == findEnumForBlockReturn(CO->getFalseExpr()))
+        return ED;
+    return 0;
+  }
+
+  // (implicitly:)
+  //   - it is an implicit integral conversion applied to an
+  //     enumerator-like expression of type T or
+  if (ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(E)) {
+    // We can only see integral conversions in valid enumerator-like
+    // expressions.
+    if (ICE->getCastKind() == CK_IntegralCast)
+      return findEnumForBlockReturn(ICE->getSubExpr());
+    return 0;
+  }
+
+  //   - it is an expression of that formal enum type.
+  if (const EnumType *ET = E->getType()->getAs<EnumType>()) {
+    return ET->getDecl();
+  }
+
+  // Otherwise, nope.
+  return 0;
+}
+
+/// Attempt to find a type T for which the returned expression of the
+/// given statement is an enumerator-like expression of that type.
+static EnumDecl *findEnumForBlockReturn(ReturnStmt *ret) {
+  if (Expr *retValue = ret->getRetValue())
+    return findEnumForBlockReturn(retValue);
+  return 0;
+}
+
+/// Attempt to find a common type T for which all of the returned
+/// expressions in a block are enumerator-like expressions of that
+/// type.
+static EnumDecl *findCommonEnumForBlockReturns(ArrayRef<ReturnStmt*> returns) {
+  ArrayRef<ReturnStmt*>::iterator i = returns.begin(), e = returns.end();
+
+  // Try to find one for the first return.
+  EnumDecl *ED = findEnumForBlockReturn(*i);
+  if (!ED) return 0;
+
+  // Check that the rest of the returns have the same enum.
+  for (++i; i != e; ++i) {
+    if (findEnumForBlockReturn(*i) != ED)
+      return 0;
+  }
+
+  // Never infer an anonymous enum type.
+  if (!ED->hasNameForLinkage()) return 0;
+
+  return ED;
+}
+
+/// Adjust the given return statements so that they formally return
+/// the given type.  It should require, at most, an IntegralCast.
+static void adjustBlockReturnsToEnum(Sema &S, ArrayRef<ReturnStmt*> returns,
+                                     QualType returnType) {
+  for (ArrayRef<ReturnStmt*>::iterator
+         i = returns.begin(), e = returns.end(); i != e; ++i) {
+    ReturnStmt *ret = *i;
+    Expr *retValue = ret->getRetValue();
+    if (S.Context.hasSameType(retValue->getType(), returnType))
+      continue;
+
+    // Right now we only support integral fixup casts.
+    assert(returnType->isIntegralOrUnscopedEnumerationType());
+    assert(retValue->getType()->isIntegralOrUnscopedEnumerationType());
+
+    ExprWithCleanups *cleanups = dyn_cast<ExprWithCleanups>(retValue);
+
+    Expr *E = (cleanups ? cleanups->getSubExpr() : retValue);
+    E = ImplicitCastExpr::Create(S.Context, returnType, CK_IntegralCast,
+                                 E, /*base path*/ 0, VK_RValue);
+    if (cleanups) {
+      cleanups->setSubExpr(E);
+    } else {
+      ret->setRetValue(E);
     }
   }
-
-  // Special case for the first return statement we find.
-  // The return type has already been tentatively set, but we might still
-  // have an alternate type we should prefer.
-  if (AlternateType.isNull())
-    AlternateType = LooseType;
-
-  if (Ctx.hasSameType(DeducedType, StrictType)) {
-    // FIXME: The loose type is different when there are constants from two
-    // different enums. We could consider warning here.
-    if (AlternateType != Ctx.DependentTy)
-      if (!Ctx.hasSameType(AlternateType, LooseType))
-        AlternateType = Ctx.VoidTy;
-    return true;
-  }
-
-  if (Ctx.hasSameType(DeducedType, LooseType)) {
-    // Use DependentTy to signal that we're using an alternate type and may
-    // need to add casts somewhere.
-    AlternateType = Ctx.DependentTy;
-    return true;
-  }
-
-  if (Ctx.hasSameType(AlternateType, StrictType) ||
-      Ctx.hasSameType(AlternateType, LooseType)) {
-    DeducedType = AlternateType;
-    // Use DependentTy to signal that we're using an alternate type and may
-    // need to add casts somewhere.
-    AlternateType = Ctx.DependentTy;
-    return true;
-  }
-
-  return false;
 }
 
 void Sema::deduceClosureReturnType(CapturingScopeInfo &CSI) {
   assert(CSI.HasImplicitReturnType);
 
+  // C++ Core Issue #975, proposed resolution:
+  //   If a lambda-expression does not include a trailing-return-type,
+  //   it is as if the trailing-return-type denotes the following type:
+  //     - if there are no return statements in the compound-statement,
+  //       or all return statements return either an expression of type
+  //       void or no expression or braced-init-list, the type void;
+  //     - otherwise, if all return statements return an expression
+  //       and the types of the returned expressions after
+  //       lvalue-to-rvalue conversion (4.1 [conv.lval]),
+  //       array-to-pointer conversion (4.2 [conv.array]), and
+  //       function-to-pointer conversion (4.3 [conv.func]) are the
+  //       same, that common type;
+  //     - otherwise, the program is ill-formed.
+  //
+  // In addition, in blocks in non-C++ modes, if all of the return
+  // statements are enumerator-like expressions of some type T, where
+  // T has a name for linkage, then we infer the return type of the
+  // block to be that type.
+
   // First case: no return statements, implicit void return type.
   ASTContext &Ctx = getASTContext();
   if (CSI.Returns.empty()) {
@@ -308,6 +388,17 @@
   if (CSI.ReturnType->isDependentType())
     return;
 
+  // Try to apply the enum-fuzz rule.
+  if (!getLangOpts().CPlusPlus) {
+    assert(isa<BlockScopeInfo>(CSI));
+    const EnumDecl *ED = findCommonEnumForBlockReturns(CSI.Returns);
+    if (ED) {
+      CSI.ReturnType = Context.getTypeDeclType(ED);
+      adjustBlockReturnsToEnum(*this, CSI.Returns, CSI.ReturnType);
+      return;
+    }
+  }
+
   // Third case: only one return statement. Don't bother doing extra work!
   SmallVectorImpl<ReturnStmt*>::iterator I = CSI.Returns.begin(),
                                          E = CSI.Returns.end();
@@ -316,47 +407,25 @@
 
   // General case: many return statements.
   // Check that they all have compatible return types.
-  // For now, that means "identical", with an exception for enum constants.
-  // (In C, enum constants have the type of their underlying integer type,
-  // not the type of the enum. C++ uses the type of the enum.)
-  QualType AlternateType;
 
   // We require the return types to strictly match here.
+  // Note that we've already done the required promotions as part of
+  // processing the return statement.
   for (; I != E; ++I) {
     const ReturnStmt *RS = *I;
     const Expr *RetE = RS->getRetValue();
-    if (!checkReturnValueType(Ctx, RetE, CSI.ReturnType, AlternateType)) {
-      // FIXME: This is a poor diagnostic for ReturnStmts without expressions.
-      Diag(RS->getLocStart(),
-           diag::err_typecheck_missing_return_type_incompatible)
-        << (RetE ? RetE->getType() : Ctx.VoidTy) << CSI.ReturnType
-        << isa<LambdaScopeInfo>(CSI);
-      // Don't bother fixing up the return statements in the block if some of
-      // them are unfixable anyway.
-      AlternateType = Ctx.VoidTy;
-      // Continue iterating so that we keep emitting diagnostics.
-    }
-  }
 
-  // If our return statements turned out to be compatible, but we needed to
-  // pick a different return type, go through and fix the ones that need it.
-  if (AlternateType == Ctx.DependentTy) {
-    for (SmallVectorImpl<ReturnStmt*>::iterator I = CSI.Returns.begin(),
-                                                E = CSI.Returns.end();
-         I != E; ++I) {
-      ReturnStmt *RS = *I;
-      Expr *RetE = RS->getRetValue();
-      if (RetE->getType() == CSI.ReturnType)
-        continue;
+    QualType ReturnType = (RetE ? RetE->getType() : Context.VoidTy);
+    if (Context.hasSameType(ReturnType, CSI.ReturnType))
+      continue;
 
-      // Right now we only support integral fixup casts.
-      assert(CSI.ReturnType->isIntegralOrUnscopedEnumerationType());
-      assert(RetE->getType()->isIntegralOrUnscopedEnumerationType());
-      ExprResult Casted = ImpCastExprToType(RetE, CSI.ReturnType,
-                                            CK_IntegralCast);
-      assert(Casted.isUsable());
-      RS->setRetValue(Casted.take());
-    }
+    // FIXME: This is a poor diagnostic for ReturnStmts without expressions.
+    // TODO: It's possible that the *first* return is the divergent one.
+    Diag(RS->getLocStart(),
+         diag::err_typecheck_missing_return_type_incompatible)
+      << ReturnType << CSI.ReturnType
+      << isa<LambdaScopeInfo>(CSI);
+    // Continue iterating so that we keep emitting diagnostics.
   }
 }
 
diff --git a/test/SemaObjC/blocks.m b/test/SemaObjC/blocks.m
index 9926b08..dd659ad 100644
--- a/test/SemaObjC/blocks.m
+++ b/test/SemaObjC/blocks.m
@@ -75,10 +75,11 @@
 
 
 // In C, enum constants have the type of the underlying integer type, not the
-// enumeration they are part of. We pretend the constants have enum type when
-// they are mixed with other expressions of enum type.
+// enumeration they are part of. We pretend the constants have enum type if
+// all the returns seem to be playing along.
 enum CStyleEnum {
-  CSE_Value = 1
+  CSE_Value = 1,
+  CSE_Value2 = 2
 };
 enum CStyleEnum getCSE();
 typedef enum CStyleEnum (^cse_block_t)();
@@ -92,7 +93,9 @@
   a = ^{ // expected-error {{incompatible block pointer types assigning to 'cse_block_t' (aka 'enum CStyleEnum (^)()') from 'int (^)(void)'}}
     return 1;
   };
-  a = ^{ // expected-error {{incompatible block pointer types assigning to 'cse_block_t' (aka 'enum CStyleEnum (^)()') from 'int (^)(void)'}}
+
+  // No warning here.
+  a = ^{
     return CSE_Value;
   };
 
@@ -114,6 +117,15 @@
     else
       return 1;
   };
+
+  // rdar://13200889
+  extern void check_enum(void);
+  a = ^{
+    return (arg ? (CSE_Value) : (check_enum(), (!arg ? CSE_Value2 : getCSE())));
+  };
+  a = ^{
+    return (arg ? (CSE_Value) : ({check_enum(); CSE_Value2; }));
+  };
 }